This invention relates to controls using an electronic control system for automatic transmissions of the four-forwardspeed type equipped with a hydraulic torque converter.
All conventional controls for automatic transmissions have depended upon hydraulic control systems for their shift control. On the other hand, controls employing electronic control systems have already been proposed which positively determine the shifting points by electrically determining the vehicle speed and throttle opening and setting the shift pattern which permit the power train design to meet sports-car-like specifications. Controls of the electronically controlled type, when incorporating an electric control system, tend to be expensive. When the number of shift positions is limited, e.g., to three speed positions, the number of parts required for such controls is correspondingly small and it poses no practical problem. However, with a greater number of shift positions, e.g., four or five speed positions, a larger number of parts will be needed, thereby giving rise to an economic disadvantage. In addition, the increased number of shift positions will complicate the shift pattern and call for greater precision in the sensing of the vehicle-speed and throttle-opening and of the shift pattern setting. In this connection, the provision of an electric control system is highly advantageous.
The present invention therefore has for its object to simplify the construction of controls of the electronically controlled type for four-forward-speed automatic transmissions.